In membrane-type fluid flow transfer devices, one fluid flows past one surface of a semipermeable membrane, another fluid flows past the other surface, and transfer of matter through the membrane from one fluid to the other occurs.
U.S. Pat. Nos. 4,163,721; 4,165,287; 4,239,625; and 4,246,121, which are hereby incorporated by reference, disclose such a device designed for use as a blood dialyzer. It has a pleated membrane potted within a housing to define alternate blood and dialysate passages, and a pleated, fluid-transmissive spacer netting is placed in the lower-pressure dialysate passages on the dialysate side of the membrane. During construction of the device, the entrances to the blood passages between adjacent membrane fold edges are maintained closed while potting material is injected between the housing and the fold edges to avoid blockage of the blood passages by the potting. One disclosed method of maintaining the entrances closed involves increasing the pressure on the dialysate side of the membrane. Another disclosed method involves painting an adhesive primer on the membrane fold edges to bond adjacent edges together.
In adapting the above-described fluid flow transfer device for use in a blood oxygenator, it was decided to place spacers between folds on the blood side of the membrane, the side potted to the housing, to facilitate the opening of the blood channels during use. This use of spacer in the blood passages, however, prevented maintaining the entrances to blood passages closed during potting by the two methods described above.